Low pressure refrigeration system

ABSTRACT

A liquid refrigerated recirculation system is disclosed in which overfeed liquid from the evaporators is collected in an accumulator, alternately drained to one or the other of two pumper drums, and recirculated to the evaporators with all makeup liquid which is supplied to the pumper drums and provides the recirculation pressure.

States Patent 1191 Elite 1|? Watkins Nov. 19, 1974 [54] LOW PRESSUREREFRIGERATION 3,353,367 ll/l967 Garland 62/174 SYSTEM [75] Inventor:John E. Watkins, Maywood, ill. Primary Examiner-Meyer Peru" Attorney,Agent, or Firm-Wolfe, Hubbard, Leydig, [73] Ass1gnee: SuccessorCorporatlon, Maywood, Voit & Osann [22] Filed: Dec. 4, 1972 [57]ABSTRACT [21] Appl' 311772 A liquid refrigerated recirculation system isdisclosed in which overfeed liquid from the evaporators is co]- [52] US.Cl. 62/ 174, 62/512 lected in an accumulator, alternately drained to oneor [51] Int. Cl F25b 41/00 the other of two pumper drums, andrecirculated to [58] Field of Search 62/149, 174, 512 the evaporatorswith all make-up liquid which is supplied to the pumper drums andprovides the recircula- [56] References Cited tion pressure.

UNITED STATES PATENTS 3 Claims, 1 Drawing Figure 3,315,484 4/l967 Ross62/174 LOW PRESSURE REFRIGERATION SYSTEM The invention relates torefrigeration systems generally, and more particularly to large capacityrefrigeration systems suitable for commercial installations such as coldstorage rooms, ice skating rinks, and other like refrigerationapplications.

This invention is an improvement on gas pumping recirculation systems asdisclosed in my prior US. Pat. Nos. 2,590,741; 2,931,191 and 2,952,137.The advantages of gas pumping recirculation systems are now well knownin the art. Such systems are reliable and require little maintenanceover long periods of time since mechanical pumps for circulating liquidrefrigerant are dispsensed with. Such systems when constructed andoperated in accordance with the teachings of my patents provideoperating economies because of reduced power consumption sincecondensing pressures are allowed to rise and fall with the ambienttemperature of the cooling medium, while liquid refrigerant is fed underpressure to the evaporators thus taking advantage of lower condensingtemperatures and pressures in the cooler periods of the year andfollowing the weather.

In the low pressure refrigeration system of said US. Pat. No. 2,952,137,the feed liquid refrigerant is subcooled and completely freed of flashgas, and with such, subcooled liquid being furnished to the evaporatorcoils, the coils operate at higher efficiency. By providing for therecirculation of an amount of liquid refrigerant which is in excess ofthe evaporating capacity of the evaporators, at a steady and easily setliquid pressure below the condensing pressure, the system may beoperated to allow condensing pressures to rise and fall according to theambient condensing medium, thus reducing compressor power requirementsto a minimum and reducing the cost of operation at the system.

The principal object of this invention is to provide improvements in therefrigeration system of US. Pat. No. 2,952,137 which will afford theadvantages and features of that system with less costly equipmentcomponents, thus providing an improved system at less initial cost.

Another object is to provide a gas pumping recirculating system in whichthe evaporators are operated in a flooded condition, and wherein theliquid overfeed is recirculated via a pair of alternatively cycledpressurized pumper drums while the liquid from the condenser(corresponding to the refrigerant boiled off primarily in the systemevaporators) is fed to the evaporators under a predeterminedintermediate feed pressure without first being dropped to suctionpressure. A related object is to reduce thermodynamic losses due to gasloss in a recirculating system of the general type of my prior US. Pat.No. 2,952,137 which is characterized by a pair of pumper drums forliquid overfeed recirculation, and to reduce other losses by providing amore compact arrangement of pumper drums and associated tanks and liquidlines.

A further object is to provide a system of this general type requiringless refrigerant charge and thus less costly to start-up.

Another object is to provide a system which is capable of furnishing astream of subcooled liquid refrigerant to the evaporators made up ofrecirculated liquid combined with a steady stream of primary liquid fromthe condenser.

Turning now to the drawing, it illustrates a refrigeration systemincorporating the invention.

Referring to the drawing, there is diagrammatically illustrated acentral unit 10 for supplying liquid refrigerant, such as one of theFreons or Ammonia, to evaporator coils 12. The evaporator coils may bein the floor of an ice skating rink, in a cold storage room, or in otherlike refrigeration applications. In this system, the evaporators 12 arepreferably operated in flooded condition, receiving preferably on theorder of twice the liquid refrigerant evaporated in the coils, and theliquid overfeed is recirculated to the evaporators while the refrigerantgas is returned from the evaporators through a suction or return line 22and carried to the compressors. Typically, the supply and return lines20, 22 terminate in a plant power room where the central refrigerantunit 10 shown in the drawing is located adjacent the compressors (notshown). In some installations a plurality of central refrigeration unitsmay be located throughout the plant and served by a common set ofcompressors and condenser but for illustration it may be assumed thatthe central refrigerant unit illustrated is located in a power roomclose to the compressors, while the condenser is located outside theplant connected by lines to the compressors and the centralrefrigeration unit.

As shown in the drawing, the central refrigeration unit 10 comprises anaccumulator tank 24 and a pair of pumper drums 26, 28. These areassembled in a compact unit in practice, but are shown in their generalphysical relationship in the drawing. The accumulator tank 24 isinterposed in the suction line 22 and receives liquid refrigerantoverfeed from the evaporators 12, while spent refrigerant gas is carriedfrom the accumulator tank to the compressors through the inlet line 30.Pressurized refrigerant gas discharged from the compressors is deliveredby way of a hot gas outlet line (not shown) to the condenser (not shown)wherein the refrigerant is cooled and liquified. The liquid refrigerantthen passes either to a receiver (not shown) in which the refrigerant istemporarily stored, and then through a connecting line 32 to the centralunit, or directly from the condenser to the unit through said line 32where the accumulator tank is made large enough to function as the plantreceiver.

For recirculation of the liquid refrigerant overfeed which collects inthe accumulator tank 24, this liquid drains continuously by gravity flowto one or the other of the two pumper drums 26, 28, the accumulatorbeing connected through separate drain lines 34, 36, illustratively, toeach of the pumper drums for this purpose. Check valves 38, 40 areinterposed in these drain lines 34, 36, permitting flow of liquid fromthe accumulator to the tank but preventing reverse flow. Both pumperdrums 26, 28 are connected to the suction side of the system by ventlines 42, 44 leading from the pumper drums to the accumulator and havingvent solenoid valves 46, 48 in these lines. The vent solenoid valves 46,48 are alternately operable to vent one pumper drum or the other tosuction so as to allow filling the pumper drum by gravity with liquidrefrigerant from the accumulator tank. Liquid refrigerant will drainfrom the accumulator to either pumper drum, depending on which ventsolenoid valve is open to equalize the pressures in the accumulator andthe pumper drum being filled.

Provision is made for introducing pressurized refrigerant into thepumper drums alternately to force the liquid refrigerant in the drumsthrough the supply line to the evaporators and thereby recirculate theliquid refrigerant overfeed. Control means are provided so that thepumper drums are alternately filled and emptied. The control meansherein shown includes solenoid operated valves 50, 52 located in branchlines 54, 56, which carry pressurized refrigerant through the lowersections of the vent lines 42, 44 to the pumper drums. The controlwiring is such that one vent solenoid valve (46 or 48) and one pressurecontrol solenoid valve (50, 52) are wired in parallel while the otherpair of solenoid valves are similarly wired in parallel. The two sets ofsolenoid valves may be operated by a timer or by liquid level switcheslocated in the pumper drums. The latter type of control system andwiring is illustrated in my prior U.S. Pat. No. 2,952,137 and hence notrepeated here. The operation is such that when the vent solenoid valve46 for pumper drum 26 is open, the pressure solenoid valve 50 thereforis closed allowing liquid to drain into the drum 20 from the accumulator24 through the drain line 34. During the filling cycle for the pumperdrum 26, the pumper drum 28 is on the feed cycle with its associatedvent solenoid valve 48 closed and the pressure solenoid valve 52 openbringing over pressurized refrigerant to force the liquid out of thepumper drum 28 through its discharge line 58 and a check valve 60 into afeed line 62 connecting with the supply line 20 for the plantevaporators 12.

According to the present invention, the stream of liquid refrigerantrecirculated to the evaporators 12 from the accumulator 24 via thepumper drums 26, 28 is augmented by combining therewith and feeding tothe evaporators a stream of primary liquid received from the condenser.As herein shown this is achieved by feeding primary liquid refrigerantfrom the condenser and combining the primary liquid in the pumper drum26, 28 during each pumping cycle of the drum with the liquid refrigeranttherein. In carrying out the invention in its preferred form, make-upliquid refrigerant suplied from the condenser at a rate substantiallyequivalent to the actual evaporator load is fed to the evaporators at acontrolled intermediate pressure, which is greater than suction pressureby an amount sufficient to overcome the liquid line losses and providean adequate feed rate for the evaporators, and is less than condensingpressure. The refrigerant overfeed is recirculated via the pumper drumsand pumped at the same intermediate pressure.

In the system disclosed in my prior patent 2,952,137, the primary liquidrefrigerant from the condenser (or separate receiver if there is one) iscarried through a liquid feed line to the accumulator, the liquid linehaving an orifice to flash down the liquid to suction pressure andthereby provide liquid in the accumulator at suction pressure. Theprimary liquid and the liquid overfeed from the evaporators is combinedin the accumulator, and then drained alternately to one or the other ofa pair of pumper drums which are pressurized alternately from the highside of the system to provide pumping pressure to force the liquidrefrigerant alternately from the pumper drums through the supply linesto evaporators. According to the present invention, primary liquidrefrigerant from the condenser (or receiver if there is one) is fed notto the accumulator but preferably to the pumper drums alternately at areduced pressure (compared to condenser pressure) providing thepressurization for the pumper drums.

The present invention provides an initial equipment cost savings becausewith smaller and less costly pumper drums and associated drainconnections and valves, the system affords substantially the same operating advantages provided by the system of my prior art US. Pat. No.2,952,137. Furthermore, thermodynamic losses are less with the presentsystem since the primary liquid from the condenser is flashed down to anintermediate pressure greater than suction pressure resulting in lessgas loss.

For augmenting during each pumping cycle the liquid feed from a pumper(26 or 28) drum with direct liquid feed from the condenser, whichsimultaneously supplies the pumping pressure for feeding the collectedliquid from the pumper drum, the liquid line 32 from the condenser (orreceiver if there is one) is connected to dump the liquid into an oilstill 62, and a line 64 carries the primary liquid from the oil still 62through a valve 66 into a separator tank 68. From the top of theseparator tank 68 a connection is made through a regulator valve 70 tothe suction side of the system by a connection 71 to the accumulatortank 24. In the separator tank 68, the flash gas resulting from thepressure drop at the orifice of the valve 66 is released in part throughthe regulator valve 70 into the accumulator tank 24 which is maintainedat suction pressure. By means of the regulator valve 70 a predeterminedpressure is maintained in the separator tank 68 which is the feedpressure for the system. This predetermined pressure may be either afixed pressure, if the regulator valve 70 is of the conventional springbiased type to hold a fixed back pressure, or a predetermineddifferential pressure above suction pressure if the regulator valve 70is a conventional differential pressure valve with a connection to sensesuction pressure. The pressure in the separator tank is determined bythe pressure regulator valve 70 and this pressure is the liquid pumpingpressure for the system, since the liquid (or mixed phase fluid) in theseparator tank is carried from the separator tank 68 through a dischargeline 72 to one of the pumper drums 26 or 28 via one of the branch lines(54 or 56) and one of the vent lines (42 or 44) depending on whichpressure solenoid valve (50 or 52) is open. By adjustment of theregulator valve 70, the system affords wide regulation of pumpingpressure and thus liquid supply pressure to the house evaporator overthe range between suction and compressor discharge pressure. in thisimproved system, the pressurizing of the pumper drums alternately isachieved by supplying a primary stream of pressurized refrigerant fromthe condenser which has been reduced to an intermediate pumping pressureby means of the pressure reduction across the orifice of the valve 66and the control afforded by the pressure regulating valve 70, and thisprimary stream of pressurized refrigerant from the condenser is used toaugment the recirculation of liquid overfeed collected in the pumperdrums.

A further feature of this arrangement is the provision for oilseparation from the liquid refrigerant, particularly important in thecase where the freons are used as the refrigerant. For oil separation,interposed in the line 32 from the condenser is the oil still 62 towhich the-warm primary liquid from the condenser is supplied. The liquidfrom the condenser drains into the oil still 62 and discharges from thebottom of the oil still through the discharge line 72. Within the oilstill is a coil 74 (shown in dashed lines) draining oil to an oilreceiver (not shown) and supplied with oil rich liquid refrigerant fromthe pumper drums and the accumulator through an oil line 75. The warmliquid refrigerant from the condenser as it passes over the coil in theoil still, vaporizes the refrigerant in the coil which is then releasedto the suction side of the system. The distilled oil is drained to theoil receiver and recirculated to the crankcases of the compressors.

A liquid level sensing device 76 in the wall of the oil still 62 sensesthe presence of liquid refrigerant received therein through the line 32from the condenser, and controls the operation of the valve 66 so as toclose down that valve when the device 76 senses a lowering of the liquidin the still. A bypass 80 around the valve 66 may be provided with avalve 82 to control flow through the bypass.

The pressurized refrigerant after expansion through the valve 66 and atthe reduced pressure predetermined by the setting of the pressurecontrol valve 70 is then carried alternately to the pumper drums 26 or28 and is a stream of primary make-up pressurized refrigerant. Thatstream is combined in the pumper drums with the recirculated liquidrefrigerant collected therein and discharged on the feee cycle througheither the discharge line 58 for the pumper drum 28 or the dischargeline 59 and check valve 61 for the pumper drum 26 to the feed line 20.It will thus be seen that the pumper drums, accumulator and associatedlines and controls forms a recirculating system for liquid refrigerantoverfeed passing through the evaporator, while all make-up pressurizedrefrigerant is supplied from the compressor and condenser, and combinedwith the liquid refrigerant recirculated via the recirculation systemand fed to the evaporator.

I claim as my invention:

1. In a refrigeration system having an evaporator and operative tooverfeed the evaporator with liquid refrigerant in excess of thatevaporated, a compressor, a suction line connecting the return side ofsaid evaporator with the suction inlet of said compressor, anaccumulator tank interposed in said suction line operative to collectliquid refrigerant overfeed passing through the evaporator whilepermitting gaseous refrigerant to return to the compressor, a condenserconnected to the outlet of said compressor operative to cool and liquifycompressed refrigerant gas received from the compressor, and a systemconnected to the accumulator and the for pumping the liquid refrigeranttherein to the evaporator, the improvement comprising:

means including a pressure reducing connection and v a pressure controlvalve connected to receive and operative to reduce the pressure of allof said refrigerant from the condenser to a predetermined pressure toprovide a stream of primary make-up pressurized refrigerant, and furtherincluding means for carrying all of said stream of primary make-uppressurized refrigerant to said pumper drums, combining said stream withoverfeed liquid refrigerant in said pumper drums and utilizing saidstream for alternately pressurizing said pumper drums for feedingrefrigerant to said evaporator. 2. In a refrigeration system, theimprovement according to claim 1 wherein said means for carrying thestream of primary make-up pressurized refrigerant includes connectionsfor feeding primary pressurized refrigerant alternately to said pumperdrums and said stream of primary pressurized refrigerant simultaneouslypressurizes said pumper drums and is combined with the overfeed liquidrefrigerant collected therein.

3. In a refrigeration system having an evaporator and operative tooverfeed the evaporator with liquid refrigerant in excess of thatevaporated, a compressor, a suction line connecting the discharge sideof said evaporator with the suction inlet of said compressor, and acondenser connected to the outlet of said compressor operative to cooland liquify compressed refrigerant gas received from the compressor, thecombination comprising:

a recirculating system connected to the evaporator for recirculating theliquid refrigerant overfeed passing through the evaporator including anaccumulator tank interposed in said suction line operative to collectliquid refrigerant overfeed passing through the evaporator whilepermitting gaseous refrigerant to return to the compressor, a pair ofpumper drums connected to said accumulator tank for alternatelyreceiving liquid refrigerant therefrom by gravity,

means including a pressure reducing connection and a pressure controlvalve connected to receive and operative to reduce the pressure of allmake-up liquid refrigerant from the condenser to a predeterminedpressure to provide a stream of primary make-up pressurized refrigerant;and

means for carrying all of said stream of primary make-up pressurizedrefrigerant to said pumper drums and alternately pressurizing said drumswith said stream for pumping the liquid refrigerant

1. In a refrigeration system having an evaporator and operative tooverfeed the evaporator with liquid refrigerant in excess of thatevaporated, a compressor, a suction line connecting the return side ofsaid evaporator with the suction inlet of said compressor, anaccumulator tank interposed in said suction line operative to collectliquid refrigerant overfeed passing through the evaporator whilepermitting gaseous refrigerant to return to the compressor, a condenserconnected to the outlet of said compressor operative to cool and liquifycompressed refrigerant gas received from the compressor, and a systemconnected to the accumulator and the evaporator for recirculating theliquid refrigerant overfeed collected in the accumulator including apair of pumper drums connected to said accumulator tank for alternatelyreceiving liquid refrigerant therefrom by gravity, and means suppliedfrom the outlet of the compressor for alternately pressurizing saidpumper drums for pumping the liquid refrigerant therein to theevaporator, the improvement comprising: means including a pressurereducing connection and a pressure control valve connected to receiveand operative to reduce the pressure of all of said refrigerant from thecondenser to a predetermined pressure to provide a stream of primarymake-up pressurized refrigerant, and further including means forcarrying all of said stream of primary make-up pressurized refrigerantto said pumper drums, combining said stream with overfeed liquidrefrigerant in said pumper drums and utilizing said stream foralternately pressurizing said pumper drums for feeding refrigerant tosaid evaporator.
 2. In a refrigeration system, the improvement accordingto claim 1 wherein said means for carrying the stream of primary make-uppressurized refrigerant includes connections for feeding primarypressurized refrigerant alternately to said pumper drums and said streamof primary pressurized refrigerant simultaneously pressurizes saidpumper drums and is combined with the overfeed liquid refrigerantcollected therein.
 3. In a refrigeration system having an evaporator andoperative to overfeed the evaporator with liquid refrigerant in excessof that evaporated, a compressor, a suction line connecting thedischarge side of said evaporator with the suction inlet of saidcompressor, and a condenser connected to the outlet of said compressoroperative to cool and liquify compressed refrigerant gas received fromthe compressor, the combination comprising: a recirculating systemconnected to the evaporator for recirculating the liquid refrigerantoverfeed passing through the evaporator including an accumulator tankinterposed in said suction line operative to collect liquid refrigerantoverfeed passing through the evaporator while permitting gaseousrefrigerant to return to the compressor, a pair of pumper drumsconnected to said accumulator tank for alternately receiving liquidrefrigerant therefrom by gravity, means including a pressure reducingconnection and a pressure control valve connected to receive andoperative to reduce the pressure of all make-up liquid refrigerant fromthe condenser to a predetermined pressure to provide a stream of primarymake-up pressurized refrigerant; and means for carrying all of saidstream of primary make-up pressurized refrigerant to said pumper drumsand alternately pressurizing said drums with said stream for puMping theliquid refrigerant therein to the evaporators.